1. Technical Field
The present invention relates to a liquid detector that can suitably detect an amount of remaining liquid (ink) in a liquid consuming apparatus such as an inkjet printing apparatus and a liquid container having the liquid detector.
2. Related Art
As a representative example of a liquid consuming apparatus, there is an inkjet printing apparatus having an inkjet print head for printing an image. Other liquid ejecting apparatuses may include an apparatus having a coloring material ejecting head used for manufacturing a color filter and the like of a liquid display, an apparatus having an electrode material (conductive paste) ejecting head used for forming electrodes of an organic EL display, a field emission display (FED), and the like, an apparatus having a biological organic material ejecting head used for manufacturing a bio chip, and an apparatus having a sample ejecting head as a precise pipette.
In the inkjet printing apparatus as the representative example of the liquid consuming apparatus, an inkjet print head having a pressure generator pressurizing a pressure generating chamber and nozzle orifices ejecting the pressurized ink as ink droplets is mounted on a carriage. By endlessly supplying the ink in an ink container to the print head through a flow channel, a printing operation can be continuously performed. The ink container is constructed as a detachable cartridge that can be replaced by a user when the ink is completely consumed.
There is a method of managing ink consumption by integrating the number of ink droplets emitted from the print head or the amount of ink sucked in maintenance by software or a method of managing when the ink is actually consumed by a predetermined amount by attaching a liquid level detecting electrode to the ink cartridge, as a method of managing the ink consumption of an ink cartridge.
However, the method of managing the ink consumption by integrating the number of ejected ink droplets or the amount of ink by software causes the following problem. The head may eject ink droplets with non-uniformity in weight. The non-uniformity in weight of the ink droplets does not affect the image quality but the ink with a margin is filled in the ink cartridge in consideration of accumulation of errors in ink consumption due to the non-uniformity. Accordingly, there is a problem that the ink corresponding to the margin remains in some apparatuses.
On the other hand, in the method of managing when the ink is consumed by the use of an electrode, since the actual amount of remaining ink can be detected, it is possible to manage the amount of remaining ink with high reliability. However, since the detection of the ink level depends on the conductivity of the ink, the kinds of ink detectable are limited, thereby complicating the sealing structure of the electrode. Since precious metals with excellent conductivity and anti-corrosion are usually used as the material of the electrode, the cost for manufacturing the ink cartridge is enhanced. Since two electrodes should be necessarily formed, the number of manufacturing processes increases, thereby increasing the manufacturing cost.
Therefore, to solve the above-mentioned problems, a piezoelectric device (herein, referred to as a sensor unit) is disclosed in JP-A-2001-146030. The sensor unit monitors the amount of ink remaining in the ink cartridge by the use of the resonance frequency of a residual vibration signal resulting from the residual vibration (free vibration) of a vibrating plate after forcible vibration when the ink remains and does not remain in a sensor cavity opposed to the vibrating plate having a piezoelectric element formed thereon.
In JP-A-2006-281550, a metal sensor base mounted with a sensor chip including a piezoelectric element is sealed in a concave portion of the unit base by a film, and is then arranged and assembled. The sensor base of the unit base is disposed to face an ink outflow channel of an ink container. Here, the unit base is disposed liquid-tight with respect to the ink container by the use of sealing rubber. In order to guarantee the liquid-tight property of the sealing rubber, a spring pressing the unit base against the ink container is provided.
The sensor chip is electrically connected to a circuit board held in the unit base. Here, the relay terminal electrically connecting the sensor chip to the circuit board needs to have a shape that is reliably fixed to the unit base and that guarantees the electrical connection in a small defined space. Known terminal structures are disclosed in JP-A-2001-57204, JP-A-5-52866, and JP-A-2003-346931.
The technique disclosed in JP-A-2006-281550 can embody the detection principle disclosed in JP-A-2001-146030, but requires the unit base independently of the ink container. Accordingly, the sealing rubber and the spring are essential to liquid-tightly fix the unit base to the ink container.
Accordingly, in JP-A-2006-281550, the number of components increases and the assembly for guaranteeing the liquid-tight property of the sealing rubber is complicated.
The unit base is shaped by two colors of polypropylene and elastomer and thus the cost therefor is high.
In the terminal structures disclosed in JP-A-2001-57204, JP-A-5-52866, and JP-A-2003-346931, specific contacts as a target of the respective structures are connected, which is not suitable for the connection between the sensor chip and the circuit board parallel thereto as a target of the invention. Particularly, when the arrangement space of the relay terminal connecting the sensor chip to the circuit board is narrowed, a fixing portion for fixing the relay terminal by thermal welding and the like is guaranteed at only one position, and thus the requirement for satisfactorily guaranteeing the contact pressures on the sensor chip and the circuit board needs to be satisfied.